RSAA Colloquia / Seminars / Feast-of-Facts: Friday, 09 October 2015, 14:00-14:40; Duffield Lecture Theatre

David Nataf

"Recent Developments in the Study of Interstellar Extinction"

I review recent developments in the study of interstellar extinction, specifically findings on the wavelength-dependence of the extinction curve both within the Milky Way and toward nearby galaxies; And how these affect distance determinations to the Galactic centre, and in the context of Hubble’s constant, and toward Type Ia supernovae. Most importantly, the mean ratio of extinction in I-band to V-band is ~15% lower than previously believed - this in turn leads to a ~6% increase in the distance modulus toward M101 (the Pinwheel galaxy). For a sample of ~1,800 Galactic bulge sightlines, we find at least two degrees of freedom in the shape of the extinction curve, rather than one (e.g. R_{V}), which we confirm with a principal component analysis. We measure a mean ratio of A_{V}/A_{Ks}~ 13.50, and find a ~100% systematic offset with additional ~40% scatter in the reddening estimates from the Planck dust maps.